Raja (50) was arrested on Friday after members of the local population informed the Forest Department about the incident, they added.
Raja, of Chinaperali village near Virudhunagar, had raised maize on his two acre land which had been raided by peacocks, Forest Department officials said.
The farmer had allegedly sprinkled paddy seeds soaked in a poisonous substance around his land. Seven of the peacocks that ate the poisoned paddy died, they said. A postmortem of two of the deceased birds confirmed they had been poisoned, officials said.